The present invention relates to the structure of an electronic device including a number of printed circuit boards (PCBs) each being loaded with a number of LSIs or similar electronic parts. More particularly, the present invention is concerned with the structure of an electronic device having a layered switch circuit group e.g., a cross connect switch device constituting a node of an ATM (Asynchronous Transfer Mode) transmission network.
Generally, a cross connect switch device has a group of input switch circuits, a group of output switch circuits, and a wiring network connecting the two groups of switch circuits to each other. A group of intermediate switch circuits are interposed between the input and output switch circuit groups, depending on the required cross connecting function. In such a case, the above-mentioned wiring network is formed between the input switch circuit group and the intermediate switch circuit group and between the intermediate switch circuit group and the output switch circuit group. LSIs and other numerous electronic parts consisting of the input, intermediate and output switch circuit networks are mounted on a plurality of PCBs. The PCBs are, in turn, respectively inserted in a number of PCB connectors mounted on a single mother board. The wiring network is formed on the surface of the mother board and connected to the contacts of the PCB connectors.
The input and output switch circuit groups each has a number of unit switch circuits. Specifically, b unit switch circuits constituting the input switch circuit group each receives an input signal on any one of a input terminals and produces it on any one of c output terminals. Likewise, each of c unit switch circuits constituting the output switch circuit group receives the output signal of the input switch circuit group on any one of b input terminals and produces it on any one of d output terminals. The wiring network between the c.times.b output terminals of the b unit switch circuits of the input switch circuit network and the b.times.c input terminals of the unit switch circuits of the output switch circuit group are implemented by a number of unit wirings each connecting the n-th output terminal of the m-th unit switch of the former to the m-th input terminal of the n-th unit switch circuit of the latter. As a result, switch circuit networks having the wiring network therebetween are formed in a layered configuration.
Such a layered connection of switch circuit networks can be implemented as a simple bidimensional arrangement of the unit switch circuits and unit wirings. It follows that the layered connection is achievable if the input switch circuit group and the output switch circuit group are respectively formed on a first and a second PCB group, and then the PCB groups are mounted on a mother board on which a wiring network is printed beforehand.
In one of conventional structures of the above-described type of communication device, the mother board constitutes the back of a rack and, in this sense, it is often called a back wire board. The first and second PCB groups implementing the input and output switch circuit groups are respectively mounted on an upper half and a lower half of the mother board with the surfaces of the PCBs positioned parallel to the side walls of the rack. An electric fan is located between the two groups of PCBs for forcibly cooling them. Since the PCBs extend parallel to the side walls of the rack, i.e., parallel to the length of the mother board and, in addition, perpendicular to the surface of the mother board, the surfaces of the PCBs are free from deformation and, moreover, excessive stresses are prevented from acting on the portions of the PCBs which are connected to the mother board. In addition, the cooling effect available with the fan is enhanced since the PCBs are so oriented as to minimize the resistance to the flow of cooling air. However, since the PCB groups constituting the input and output switch circuit groups are oriented in the same direction on the mother board, the printed wiring provided on the mother board for forming the wiring network between the two switch circuit groups is complicated in configuration and, therefore, makes it difficult to realize the wiring network with a single layer printed wiring.
Another conventional structure is disclosed in U.S. Pat. No. 4,472,765. In this structure, two mother boards are arranged in a horizontal position in a rack. A first and a third PCB group are arranged one above another and in a horizontal position in a rack. The first and third PCB groups are respectively mounted on the upper mother board and the lower surface of the lower mother board and parallel to the side walls of the rack. A second PCB group is located between the two mother boards in parallel to the back of the rack. In such a structure, since the second PCB group is mounted on the mother boards in a position perpendicular to the first and third PCB groups, the configuration of the wirings on the mother boards is simple enough to implement the wiring network with a single layer printed wiring. However, this conventional scheme has a problem that it needs two mother boards and, in addition, makes it impossible for the operator to replace the PCBs at the front of the rack. The three PCB groups are each parallel to the side ealls or the back of the rack, i.e., perpendicular to the ground. Although such an arrangement is desirable from the cooling standpoint, the mother board intervening between the first and second PCB groups and the mother board intervening between the second and PCB groups not only reduce the cooling effect but also obstruct the arrangement of an electric fan for forced cooling.
It is therefore an object of the present invention to provide a structure of a cross connect switch or similar electronic device having a number of PCBs and a mother board on which the PCBs are mounted, which structure simplifies the configuration of a printed wiring on the mother board without degrading the cooling effect on electronic parts mounted on the PCBs or the ease of maintenance and repair at the front of a rack.
An electronic device of the present invention has a rack accommodating a mother board and a first and a second PCB group mounted on the mother board. One of the first and second PCB groups is mounted on the mother board in an upper half of the rack such that the surfaces of the individual PCBs extend substantially parallel to the side walls of the rack. The other PCB group is mounted on a lower half of the rack such that the surfaces of the individual PCBs extend substantially in the horizontal direction. A third PCB group may be disposed above one of the first and second PCB groups, if necessary. Then, the PCBs of the third PCB group are mounted on the mother board with their surfaces held substantially in the horizontal position. A wiring network between the first and second (and third) PCB groups is formed on the surface of the mother board by printing. Two fans may be respectively interposed between the first and second PCB groups and between the third and first (or second) PCB groups, as needed.
With the above construction, it is possible to simplify the configuration of the wiring network on the mother board without affecting the cooling effect on the electronic parts of the PCBs or degrading the ease of maintenance and repair at the front of the rack.